In the art of industrial welding, soldering, cutting, etc., it is desirable to have a high power laser output beam positioned and oriented by a robot, comprising movable robotic arms, to form a laser beam waveguide robot system. For certain laser sources of a high power base, such as the Nd:YAG laser, which have a significant wavelength in the one micron region of the spectrum, flexible optical fiber waveguides--e.g., silica glass fibers--may be used for guiding the high power laser beam over a distance of the order of the length of a robot arm. Such fibers can be either routed inside the robot arm or attached externally to the side of the arm. At the present time, however, flexible optical fibers for guiding high power infrared laser beams--e.g., beams of ten microns wavelength from the CO.sub.2 laser--are unavailable in the single-mode form desired for robotic arms, and also such fibers tend to suffer from too much optical loss and to be too fragile for practical use. Therefore, present-day fibers cannot readily be used for guiding a CO.sub.2 laser beam. On the other hand, the CO.sub.2 infrared laser can develop significantly more power than a Nd:YAG laser, and for many applications the ten micron radiation of the CO.sub.2 laser is more suitable than the one micron Nd:YAG radiation; therefore, it is desirable to have a robot system for a CO.sub.2 laser.
Accordingly, one approach in prior art is to guide the CO.sub.2 laser beam through a suitable optical waveguide affixed to a robot, as disclosed in an article entitled, "Major Advance by British Company in Automatic Laser Processing," in Sensor Review, pp. 64-66 (April 1983). That laser robot system, known as COBRA, includes an articulated optical light-guide in conjunction with a ASEA IRb6 robot and a Ferranti CO.sub.2 laser. The light-guide is affixed onto the robot in such a manner that segments of the light-guide are aligned in a parallel configuration with corresponding segments of the robot arm. Such an alignment allows for coincidental movement of the robot arm and the light-guide which in turn minimizes the stress on the light-guide and allows for a three-dimensional range of freedom. This robot system, however, is of undesirably large size because of the large size of the robot and because of the large size of the conventional articulated arm used as a light-guide for ten micron radiation required to avoid diffraction effects. Moreover, such a simple configuration cannot be used in conjunction with robot assemblies of desirably smaller size, such as the "Microbot Alpha" robot, because such smaller robot assemblies include robot members--e.g., side shield members--which protrude outward from the body of the robot and which would obstruct the light-guide. These protruding side shield members are needed for achieving a compact overall robot assembly in which all the motors of the robot are accommodated in one place. It would therefore be desirable to have a laser robot system that can be used with a CO.sub.2 laser in conjunction with a robot assembly having protruding side shield members, such as the Microbot Alpha.
An additional problem with articulated light-guides of the conventional type (as proposed in the above-mentioned article) is a wandering of the beam that is encountered as the arm is manipulated. This effect is encountered unless (1) the input beam is launched exactly on the axis of the light-guide, and (2) the swivel angles of the articulated light-guide are precisely equal to a right angle. In practice, such a situation is not obtainable, at least for any reasonable length of time during operation, and the exact position of the output beam is unpredictable--both undesirable effects, particularly in a robotic system.
Another approach for positioning and orienting a CO.sub.2 laser beam would be to use the robot gripper of a Microbot Alpha to hold and manipulate the laser-output tip of an articulated arm assembly, that is, a light-guide divided into rigid sections with revolute joints--i.e., joints in a section which divide that section into two parts which can rotate with respect to each other about the (common) axis of that section and which thus enable the neighboring sections of the articulated light-guide arm to revolve around that axis. Reorientation of the laser beam output in this approach, however, would require complex reconfiguration of the light-guide sections, involving rotations of all revolute joints. Such complex reconfigurations of the light-guide sections would require the robot to follow a complicated path dictated by the light-guide assembly, thereby preventing a desirable continuous rotation capability of the laser-output tip. In addition, it would be necessary to attach a force and torque sensor on the robot gripper in order to ensure that the articulated light-guide arm is not damaged by stresses produced therein when the robot attempts to reconfigure the arm. However, such technology as force and torque sensors is beyond present-day state-of-the-art robotics, since even the turning of a simple two-link crank by a robot arm is a complex compliance problem not yet properly solved.